1. Field of the Invention
The present invention relates to a piezoelectric sounding body, which comprises a piezoelectric substrate and a vibrating plate mounted thereon.
2. Description of the Background Art
FIG. 2 is a side elevational view showing the structure of a piezoelectric sounding body, which comprises a piezoelectric substrate and a vibrating plate mounted thereon. Referring to FIG. 2, a piezoelectric substrate 1 of the piezoelectric sounding body is provided on both surfaces with electrode films 2a and 2b, respectively, which are mainly made by baking a layer of silver. A vibrating plate 3 made of a metal is stuck onto the electrode film 2b, which is formed on a lower surface of the piezoelectric substrate 1, through an adhesion layer 10. The adhesion layer 10 is thermocompression-bonded so as to stick the vibrating plate 3 onto the electrode film 2b which is provided on the surface of the piezoelectric substrate 1.
In general, the vibrating plate 3 is pressed against the electrode film 2b so as to be strongly in contact with its irregular surface, so that the vibrating plate 3 is bonded to the electrode film 2b through the adhesion layer 10. Thus, the vibrating plate 3 electrically conducts with the electrode film 2b.
However, such a conventional piezoelectric sounding body has the following problem:
In the piezoelectric sounding body, the electrode films 2a and 2b may be formed by a method such as sputtering or vapor deposition. According to such methods of forming electrode films, however, the electrode films 2a and 2b that are formed have relatively flat surfaces, with small irregularities formed therein. Therefore, even if the vibrating plate 3 is strongly pressed against the electrode film 2b through the adhesion layer 10, sufficient contact is not attained between the vibrating plate 3 and the electrode film 2b due to the small irregularities formed on the surface of the electrode film 2b. Thus, when the piezoelectric sounding body is used for a long time so that the adhesion layer 10 is repeatedly subjected to expansion and contraction, conduction failure can result between the vibrating plate 3 and the electrode film 2b.
In order to solve such a problem, the adhesion layer 10 may be prepared from an adhesive having conductivity. In an ordinary conductive adhesive, however, a large amount of conductive powder is dispersed and mixed in the adhesive in order to attain conductivity in both the longitudinal and transverse directions. For example, 80 to 90 percent by weight of silver powder is mixed in such a conductive adhesive. Accordingly sufficient adhesive strength cannot be attained between the adhesion layer 10 and the vibrating plate 3, while the adhesion layer 10 is inevitably increased in thickness thereby deteriorating the resonance characteristic of the piezoelectric sounding body.